It is one of the great enigmas of science: what happened before the Big Bang. To try to begin to answer it, we must imagine a completely unknown scenario: a universe without galaxies, without stars, not even atoms. Everything we know was compressed in an extremely hot and dense broth. And then the big explosion. That fleeting moment—the first second after the Big Bang—is the second most fascinating and, at the same time, most elusive episode in cosmic history.
Modern cosmology tells us that The universe began about 13.8 billion years ago from an extremely concentrated and hot state. In the first fractions of a second, energy and matter were indistinguishable, and the fundamental particles that today make up matter and forces had not yet finished “freezing” into the shapes we now recognize. This primordial moment is essential: it is where the rules that govern the evolution of the cosmos were decided, from the formation of atomic nuclei to the large-scale architecture of galaxies.
However, these first moments are difficult to study directly. Light (our main “beacon” to observe the universe) did not exist yet, and traditional astronomical methods cannot “show” us that moment. Instead, Scientists have had to resort to theoretical models, simulations and laboratory experiments that try to recreate conditions equivalent to those of the early universe.
And we might have a key. A group of physicists has managed to reproduce in the laboratory some of the conditions that existed in the first milliseconds of the universe. The place where this feat occurs is not an astronomical observatory, but the Large Hadron Collider (LHC) at CERN. This particle accelerator measuring 27 kilometers in circumference collides beams of protons at extreme speeds, generating immense energies. This allows them to recreate, in fractions of a second, an environment of temperature and density very similar to those of the newborn universe.
According to the results, published in Physics Letters Bthe authors (all members of the LHC), used particle collisions inside the accelerator to generate and observe a state of matter known as quark-gluon plasma, a kind of extremely hot and dense “soup” in which quarks (the building blocks of protons and neutrons) and the mediating particles of the strong nuclear force (the gluons) are free and not confined to individual particles.
This state is interpreted by scientists as an analogue of the universe microseconds after the Big Bangwhen matter had not yet crystallized into the composite particles we see today.
The importance of this type of experiments is enormous. Until now, we knew theoretically that a plasma of quarks and gluons existed in the first instant of the universe, but observing its properties directly had been impossible. The LHC can’t reconstruct the entire primordial universe, of course, but it can create a microscopic bubble with the same extreme physical conditions. By studying how this “soup” behaves and how it cools and transforms into more familiar particles, physicists can contrast their theoretical models with real data and thus narrow the uncertainties about what the universe was like on a subnanometer scale just after its birth.
The results suggest that the primordial plasma was surprisingly fluid and perfect in terms of internal conduction, with behaviors that defy some previous predictions. Analysis of the collisions reveals how quarks and gluons interact in this extreme phaseproviding clues about how the first stable particles formed and, by extension, how the universe evolved from that chaotic state to the relatively calm conditions that allowed the formation of atoms, stars and galaxies.
But what is this new knowledge for? We know that the universe evolves according to natural laws (gravity, nuclear forces and quantum mechanics), but many of these laws only fully manifest themselves under extreme conditions. The first second of the universe is precisely that laboratory where the fundamental forces were “indistinguishable” and the particles were captured in their most elemental form.
Understanding that phase is like reading the prologue to a very complex book: the processes that occurred there determined the relative abundance of matter and antimatter, the distribution of light elements such as hydrogen and helium, and the conditions for the first large-scale structures to form. Without understanding that first second, our narrative of the universe will always have a gap.